Transportation Defined: Geogrid

Transportation Defined: Geogrid

January 9, 2014

You know that there are layers of dirt and rock beneath the surface you drive on, but would you guess that some roads are built on top of a special material (in addition to all the dirt and rocks)?

What we’re referring to is called geogrid, which is a polymer material that is used to reinforce soil.

If the term sounds familiar, we’re glad. Because that means maybe you watched our video from August about the paving of US 89T (we definitely appreciate our devoted blog/YouTube followers!).

In that video, you can see that a geogrid material was used on that project. You can also hear a good explanation of how geogrid works with the dirt and rocks. In case you missed it…

“AB is aggregate base – it’s the gravel that goes down under the asphalt. It helps distribute the weight of the traffic that’s on the asphalt,” Resident Engineer Steve Monroe says in the video. “By using the geogrid, we can cut out two inches of that AB. The geogrid is much less expensive and easier to put down than hauling in all that extra AB.”

A closer look at geogrid on the US 89T project.

How is geogrid installed?

Once the subgrade material (that’s the layer under everything else) is prepared, a geogrid is placed on top (sometimes along with a geotextile filter fabric used to keep fine material from migrating into the aggregate base). The openings in the geogrid are meant to interlock with the granular aggregate base – check out the video above to see what we mean.

After the geogrid goes down, the aggregate base is placed and finally, paving takes place on top of all those layers.

Why does it work?

When testing determines it necessary, geogrid material can improve the ability of the subgrade to carry traffic loads and reduce rutting or pavement failure over weak soils. It does this by providing tensile strength and distributing the load from a vehicle to a wider area.

Transportation Defined is a series of explanatory blog posts designed to define the things you see on your everyday commute. Let us know if there's something you'd like to see explained ... leave a comment here on the blog or over on our Facebook page!